1. Field of the Invention
The invention relates to a voltage regulator. Particularly, the invention relates to a voltage regulator with a power-saving function and a low quiescent current.
2. Description of Related Art
In today's various consumer electronic products, a demand for various power supplies to simultaneously output a plurality of power voltages is increased. The current power supply generally has one or a plurality of voltage regulating circuits for providing required output voltages. Therefore, besides accuracy of each of the output voltages is strictly required, power consumption of the voltage regulating circuits is also one of important design considerations of the power supply.
When a voltage regulating circuit is designed, a liner regulator is generally used to implement the voltage regulating circuit. However, the liner regulator generally provides only one output mode, so that a large amount of current is generally consumed. Power consumptions of such type of the voltage regulating circuits are the same regardless of the power consumed by instantaneous loads. Namely, a quiescent current consumed by the linear regulator during operation is a fixed value. Therefore, when an external load driven by the voltage regulating circuit requires a large output current, the voltage regulating circuit consumes the fixed quiescent current, and when the output current required by the external load is decreased, the quiescent current consumed by the voltage regulating circuit is still maintained fixed, so that extra energy is consumed.
It should be noticed that the greater an input voltage received by the linear regulator is, the lower the output current thereof has to be, so as to prevent damaging a power amplifier in the linear regulator. However, current driving capability of the linear regulator is accordingly limited, and demand of the external load having a lighter or heavier variation cannot be satisfied.